Antiviral agents

ABSTRACT

This invention relates to compounds of formula I 
                         
their salts, and pharmaceutically acceptable derivatives thereof, pharmaceutical compositions comprising these compounds and their use in the treatment of picornavirus infections in mammals, as well as novel intermediates useful in the preparation of the compounds of formula I.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/450,005, filed Oct. 17, 2003 (371 date), now U.S. Pat. No. 7,166,604,which is a U.S. National Stage of PCT/AU01/001627, filed Dec. 18, 2001,which claims priority to Australian Application No. PR2137/00, filedDec. 18, 2000; these applications are incorporated herein by referencein their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to antiviral agents, in particular to compoundsuseful in the treatment of infections caused by Picornaviridae, such ashuman rhinovirus (HRV), and methods for their preparation. The inventionalso relates to the use of these compounds in the treatment ofpicornavirus infections and to intermediates useful in the preparationof these compounds. The compounds of the invention are especiallysuitable for use in the treatment of HRV and accordingly it will beconvenient to describe the invention in connection with these viruses.However, it is to be understood that the invention is also applicable toother viruses of the Picornavirus family.

2. Description of the Related Art

Human rhinoviruses are a member of the genus Rhinovirus of thepicornavirus family and are believed to be responsible for between 40and 50% of common cold infections. Human rhinoviruses comprise a groupof over 100 serotypically distinct viruses and accordingly antiviralactivity for multiple serotypes and potency are considered to be equallyimportant factors in drug design.

Two cellular receptors have been identified to which almost all typedHRVs bind. The major group, which comprises 91 of the more than 100typed serotypes, binds to the intracellular adhesion molecule-1 (ICAM-1)while the minor group, which comprises the rest of typed serotypes withthe exception of HRV87, binds to the low density lipoprotein receptorfamily of proteins.

Another genus of the Picornaviridae family is represented by theEnteroviruses. This genus includes polioviruses 1-3, coxsackieviruses A(23 serotypes) and B (6 serotypes), echoviruses (31 serotypes) andnumbered enteroviruses 68-71. The clinical syndromes caused byenteroviruses include poliomyelitis, meningitis, encephalitis,pleurodynia, herpangina, hand foot and mouth disease, conjunctivitis,myocarditis and neonatal diseases such as respiratory illnesses andfebrile illnesses.

Viruses of the Picornavirus family are characterized by a singlestranded (+) RNA genome encapsidated by a protein shell (or capsid)having pseudo icosahedral symmetry. The surface of the capsid contains“canyons” which surround each of the icosahedral fivefold axes, and itis believed that the cellular receptors bind to residues on the canyonfloor.

A hydrophobic pocket lies underneath the canyon within which a number ofantiviral compounds are capable of binding, sometimes with consequentialconformational changes. Some of these compounds have been shown toinhibit the uncoating of HRVs and, for some of the major receptor groupviruses, inhibition of cell receptor binding has also been demonstrated.It has also been shown that when a compound is bound within thehydrophobic capsid pocket, HRVs are more stable to denaturation by heator acids.

Examples of antipicornaviral compounds believed to act by binding withinthe hydrophobic pockets of the picornavirus capsid are described in U.S.Pat. Nos. 4,857,539, 4,992,433, 5,026,848, 5,051,515, 5,100,893,5,112,825, 5,070,090, and Australian Patent No. 628172. One compoundthat has been the subject of recent human clinical trials is ethyl4-[2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]-ethoxy]benzoate,otherwise known as “Pirodavir”. (“Intranasal Pirodavir (R77,975)Treatment of Rhinovirus Colds” F. G. Hayden, et al., AntimicrobialAgents and Chemotherapy, 39, 290-294, 1995.)

BRIEF SUMMARY OF THE INVENTION

A novel class of antiviral compounds has now been discovered which hasbeen found to exhibit particularly favorable antipicornaviralproperties.

Accordingly the present invention provides a compound of formula I

its salts, and pharmaceutically acceptable derivatives thereof where:

Het is an optionally substituted 5- or 6-membered monocyclicheterocyclic radical or an optionally substituted 9- or 10-memberedbicyclic heterocyclic radical;

A is O, S, NH, N(C₁₋₆alkyl), CH₂O, a direct bond or a bivalentheterocyclic radical of the formula

where one or more of the carbon atoms within the radicals (b-1) to (b-4)may be optionally substituted with C₁₋₆alkyl or two carbon atoms in theradicals (b-1) to (b-4) may be bridged with a C₂₋₄alkylene radical, mand n are each independently integers of 1 to 4 inclusive with theproviso that the sum of m and n in radicals (b-1) to (b-4) is 3, 4 or 5;

Z is N or CR⁶ where R⁶ is hydrogen, hydroxy, C₁₋₆alkyl, C₁₋₆alkoxy oramino;

Z′ is O, S, CHR⁷ or NR⁸ where R⁷ is hydrogen, hydroxyl, C₁₋₆alkyl,

C₁₋₆alkoxy or amino and R⁸ is hydrogen or C₁₋₆alkyl;

R⁴ is hydrogen or C₁₋₆alkyl; and

R⁵ is hydrogen, hydroxy, C₁₋₆alkyl or C₁₋₆alkoxy;

Alk is C₁₋₇alkylene or a direct bond;

W is O, S, OCH₂, a direct bond or NR⁹ where R⁹ is hydrogen or C₁₋₆alkyl;

X¹, X² and X³ are each independently selected from N and CR, where R ishydrogen, halogen, hydroxy, C₁₋₆alkyl or C₁₋₆alkoxy and

B is a five or six membered unsaturated heterocyclic ring, substitutedwith at least one substituent selected from, R¹⁰, OR¹⁰, SR¹⁰ and NR⁹R¹⁰where R¹⁰ is C₁₋₆alkyl, haloC₁₋₆ alkyl, C₁₋₆alkenyl, haloC₁₋₆alkenyl,C₁₋₆alkynyl or haloC₁₋₆alkynyl,

with the proviso that when Alk is a direct bond and A is O, S, CH₂O or adirect bond, then W is not O, S, OCH₂ or a direct bond.

The term “heterocyclic radical” as used herein refers to mono orbicyclic rings or ring systems which include one or more heteroatomsselected from N, S and O. The rings or ring systems generally include 1to 9 carbon atoms in addition to the heteroatom(s) and may be saturated,unsaturated, aromatic or pseudoaromatic.

Examples of 5-membered monocyclic heterocycles include furyl, thienyl,pyrrolyl, oxazolyl, thiazolyl, isoxazolyl, isothiazolyl, pyrazolyl,imidazolyl, triazolyl, tetrazolyl, oxadiazolyl, thiadiazolyl andexamples of 6-membered monocyclic heterocycles include pyridyl,pyrimidinyl, pyridazinyl, pyrazinyl and triazinyl, each of which may beoptionally substituted with C₁₋₆alkyl, C₁₋₆alkoxy, C₃₋₆alkynyl,C₃₋₆alkynyl, halo, hydroxy, mercapto, trifluoromethyl, amino, cyano ormono or di(C₁₋₆alkyl)amino. Examples of 9 and 10-membered bicyclicheterocycles include indolyl, benzofuranyl, benzothienyl, benzoxazolyl,benzothiazolyl, benzisoxazolyl, benzisothiazolyl, indazolyl,isoquinolinyl, quinolinyl, quinoxalinyl, cinnolinyl, phthalazinyl,quinazolinyl, benzotriazinyl and the like, each of which may beoptionally substituted with C₁₋₆alkyl, C₁₋₆alkoxy, C₃₋₆alkynyl,C₃₋₆alkynyl, halo, hydroxy, mercapto, trifluoromethyl, amino, cyano ormono or di(C₁₋₆alkyl)amino. Examples of preferred heterocyclic radicalsinclude (optionally substituted) isoxazoles, isothiazoles,1,3,4-oxadiazoles, 1,3,4-thiadiazoles, 1,2,4-oxadiazoles,1,2,4-thiadiazoles, oxazoles, thiazoles, pyridines, pyridazines,pyrimidines, pyrazines, 1,2,4-triazines, 1,3,5-triazines, benzoxazoles,benzothiazoles, benzisoxazoles, benzisothiazoles, quinolines andquinoxalines. Particular examples of the group Het are radicals offormula (a-1) to (a-14) below:

wherein R¹ is hydrogen, C₁₋₆ alkyl, halo, hydroxy, mercapto,haloC₁₋₆alkyl, amino, mono or di(C₁₋₆alkyl)amino, cyano, formyl,C₁₋₆alkoxy, hydroxyC₁₋₄ alkyl, C₁₋₄alkoxyC₁₋₄ alkyl, C₁₋₆haloalkoxy,aryloxy, C₁₋₆alkylthio, arylthio, C₁₋₆alkylsulphinyl,C₁₋₆alkylsulphonyl, arylsulphinyl, arylsulphonyl, —CH═NO—C₁₋₄alkyl,C₁₋₆alkyloxycarbonyl, C₁₋₆alkylcarbonyl or aryl;

R² and R³ are each independently selected from hydrogen, C₁₋₆alkyl,

C₁₋₆alkoxy, halo or, in radicals (a-1), (a-4), (a-7) and (a-13), R¹ andR², or R² and R³ combined may represent a bivalent radical of formula—CH═CH—CH═CH— or (CH₂)_(p) where p is an integer from 2 to 4;

Y is O or S; and

Y′ is O, S, SO or SO₂.

The term “unsaturated five or six membered heterocyclic ring” as usedherein for ring B refers to a 5 or 6 membered heterocyclic radical fusedto the six-membered ring as depicted in Formula I. The ring includes oneor more heteroatoms selected from N, S and O and will include 2 to 5carbon atoms in addition to the heteroatom(s). Two of these carbon atomsare derived from the six-membered ring to which it is attached. The ringmay be partially or fully saturated, and may be aromatic. The ring mustcontain at least one substituent selected from R¹⁰, OR¹⁰, SR¹⁰ andNR⁹R¹⁰, where R⁹ and R¹⁰ are as defined above. Examples of unsaturated5-membered heterocyclic rings include oxazole, thiazole, imidazole,1,2,3-triazole, isoxazole, isothiazole, pyrazole, furan, thiophene andpyrrole, each of which in addition to the defined substituent may beoptionally substituted with C₁₋₆alkyl, C₁₋₆alkoxy, C₃₋₆alkenyl,C₃₋₆alkynyl, halo, hydroxy, mercapto, trifluoromethyl, amino, cyano ormono or di(C₁₋₆alkyl)amino. Examples of unsaturated 6-memberedheterocyclic rings include pyridine, pyrimidine, pyrazine, pyridazineand 1,2,4-triazine, each of which in addition to the defined substituentmay be optionally substituted with C₁₋₆alkyl, C₁₋₆alkoxy, C₃₋₆alkenyl,C₃₋₆alkynyl, halo, hydroxy, mercapto, trifluoromethyl, amino, cyano ormono or di(C₁₋₆alkyl)amino. Particular examples of unsaturated five orsix membered heterocyclic rings include radicals (c-1) to (c-11) below:

where Y is O, S or NR; and R¹¹ is R¹⁰, OR¹⁰, SR¹⁰ or NR⁹R¹⁰, where R⁹and R¹⁰ are as previously defined.

In some preferred embodiments of the invention one or more of thefollowing definitions apply:

Het is a radical of formula (a-1), (a-2) or (a-8);

R¹ is hydrogen, methyl, ethyl, chloro, methoxy or trifluoromethyl;

R² and R³ are each independently hydrogen, chloro or methyl;

Y is O or S;

A is O, NH, NMe, a bond, or a radical of formula (b-1);

Z is CH or N;

Alk is C₁₋₆alkylene or a direct bond;

W is O;

X¹, X² and X³ are CH; and

B is (c-1) or (c-2).

As used herein, the term “C₁₋₆alkyl” as used alone or as part of a groupsuch as “di(C₁₋₆alkyl)amino” refers to straight chain, branched orcyclic alkyl groups having from 1 to 6 carbon atoms. Examples of suchalkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl,cyclopentyl and cyclohexyl. Similarly, C₁₋₄ alkyl refers to such groupshaving from 1 to 4 carbon atoms.

As used herein, the term “halo” as used alone or as part of a group suchas “C₃₋₆halo alkenyl” refers to fluoro, chloro, bromo and iodo groups.

As used herein, the terms “C₁₋₆alkoxy” and “C₁₋₆alkyloxy” refer tostraight chain or branched alkoxy groups having from 1 to 6 carbonatoms. Examples of C₁₋₆alkoxy include methoxy, ethoxy, n-propoxy,isopropoxy, and the different butoxy isomers.

As used herein, the term “C₃₋₆alkenyl” refers to groups formed from C₃₋₆straight chain, branched or cyclic alkenes. Examples of C₃₋₆alkenylinclude allyl, 1-methylvinyl, butenyl, iso-butenyl, 3-methyl-2-butenyl,1-pentenyl, cyclopentenyl, 1-methyl-cyclopentenyl, 1-hexenyl, 3-hexenyl,cyclohexenyl, 1,3-butadienyl, 1-4, pentadienyl, 1,3-cyclopentadienyl,1,3-hexadienyl, 1,4-hexadienyl, 1,3-cyclohexadienyl and1,4-cyclohexadienyl.

As used herein, the term “C₃₋₆alkynyl” refers to groups formed from C₃₋₆straight chain or branched groups as previously defined which contain atriple bond. Examples of C₃₋₆alkynyl include 2,3-propynyl and 2,3- or3,4-butynyl.

The term “optionally substituted” as used herein means that a group mayinclude one or more substituents which do not interfere with the bindingactivity of the compound of formula I. In some instances the substituentmay be selected to improve binding. Examples of optional substituentsinclude halo, C₁₋₄alkyl, C₂₋₄alkenyl, C₂₋₄alkynyl, C₁₋₄alkoxy,haloC₁₋₄alkyl, hydroxyC₁₋₄alkyl, C₁₋₄alkoxy, C₁₋₄alkyl, hydroxy, aryl,amino, cyano, mercapto, C₁₋₄alkylamino, C₁₋₄dialkylamino, aryloxy,formyl, C₁₋₄-alkylcarbonyl and C₁₋₄alkoxycarbonyl.

A particular group of compounds of the invention has the formula II:

wherein:

R¹ is hydrogen, C₁₋₄alkyl, halo, hydroxy, mercapto, trifluoromethyl,amino, mono or

di(C₁₋₄alkyl)amino, cyano, formyl, —CH═NO—C₁₋₄ alkyl, C₁₋₄alkoxy,C₁₋₄haloalkoxy, aryloxy, C₁₋₄alkylthio, or aryl;

Y is O, S, NH or NMe;

Z is CH or N;

Alk is C₁₋₆alkylene; and

R¹¹ is OR¹⁰ or SR¹⁰, where R¹⁰ is C₁₋₄alkyl.

Another particular set of compounds of the invention has the formulaIII:

wherein:

R¹ is hydrogen, C₁₋₄alkyl, halo, hydroxy, mercapto, trifluoromethyl,amino, mono or di(C₁₋₄alkyl)amino, cyano, formyl, —CH═NO—C₁₋₄ alkyl,C₁₋₄alkoxy, C₁₋₄haloalkoxy, aryloxy, C₁₋₄alkylthio, or aryl;

Y is O, S, NH or NMe;

Z is CH or N;

Alk is C₁₋₆alkylene; and

R¹¹ is OR¹⁰ or SR¹⁰, where R¹⁰ is C₁₋₄alkyl.

Another particular set of compounds of the invention has the formula IV:

wherein:

R¹ is hydrogen, C₁₋₄alkyl, halo, hydroxy, mercapto, trifluoromethyl,amino, mono or di(C₁₋₄alkyl)amino, cyano, formyl, —CH═NO—C₁₋₄alkyl,C₁₋₄alkoxy, C₁₋₄alkoxyC₁₋₄alkoxy, C₁₋₄haloalkoxy, aryloxy,C₁₋₄alkylthio, or aryl;

A is a bond or CH₂O;

Y is O, S, NH or NMe;

Alk is C₁₋₇alkylene;

R¹¹ is OR¹⁰ or SR¹⁰, where R¹⁰ is C₁₋₄alkyl; and

R¹² and R¹³ are each independently hydrogen, halogen, C₁₋₄alkyl orC₁₋₄alkoxy.

A particular group of compounds of the invention has the formula V

wherein:

R¹ is hydrogen, C₁₋₄ alkyl, halo, hydroxy, mercapto, trifluoromethyl,amino, mono or di(C₁₋₄alkyl)amino, cyano, formyl, —CH═NO—C₁₋₄alkyl,C₁₋₄alkoxy, C₁₋₄haloalkoxy, aryloxy, C₁₋₄alkylthio, or aryl;

Y is O, S, NH or NMc;

Z is CH or N;

Alk is C₁₋₆alkylene; and

R¹¹ is OR¹⁰ or SR¹⁰, where R¹⁰ is C₁₋₄alkyl.

A particular group of compounds of the invention has the formula VI:

wherein:

R¹ is hydrogen, C₁₋₄ alkyl, halo, hydroxy, mercapto, trifluoromethyl,amino, mono or di(C₁₋₄alkyl)amino, cyano, formyl, —CH═NO—C₁₋₄alkyl,C₁₋₄alkoxy, C₁₋₄haloalkoxy, aryloxy, C₁₋₄alkylthio, or aryl;

Y is O, S, NH or NMe;

Z is CH or N;

Alk is C₁₋₆alkylene; and

R¹¹ is OR¹⁰ or SR¹⁰, where R¹⁰ is C₁₋₄alkyl.

A particular group of compounds of the invention has the formula VII

wherein:

Het is pyridyl, pyrazinyl, thiadiazolyl, benzoxazolyl, 1,3,5-triazinyl,pyrimidinyl or quinoxalinyl, each of which may be optionally substitutedwith 1 to 3 substituents selected from halo, trifluoromethyl, C₁₋₄alkyl,C₁₋₄alkoxy or hydroxy;

Y is O, S, NH or NMe;

Z is CH or N;

Alk is C₁₋₆alkylene; and

R¹¹ is OR¹⁰ or SR¹⁰ where R¹⁰ is C₁₋₄alkyl.

A particular group of groups of the invention has the formula VIII:

wherein:

Het is pyridyl, pyrazinyl, thiadiazolyl, benzoxazolyl, 1,3,5-triazinyl,pyrimidinyl or quinoxalinyl, each of which may be optionally substitutedwith 1 to 3 substituents selected from halo, trifluoromethyl, C₁₋₄alkyl,C₁₋₄alkoxy or hydroxy;

Y is O, S, NH or NMe;

Z is CH or N;

Alk is C₁₋₆alkylene; and

R¹¹ is OR¹⁰ or SR¹⁰, where R¹⁰ is C₁₋₄alkyl.

Another group of compounds of the invention has the formula IX

wherein:

Het is pyridyl, pyridazinyl, pyrazinyl, thiadiazolyl, benzoxazolyl,1,2,4-triazinyl, 1,3,5-triazinyl, pyrimidinyl or quinoxalinyl, each ofwhich may be optionally substituted with 1 to 3 substituents selectedfrom halo, trifluoromethyl, C₁₋₄alkyl, C₁₋₄alkoxy or hydroxy;

A is a direct bond, O, NH or NMe;

Y is O, S, NH or NMe;

Alk is C₁₋₆ alkylene; and

R¹¹ is OR¹⁰ or SR¹⁰, where R¹⁰ is C₁₋₄alkyl.

Yet another group of compounds of the invention has the formula X:

wherein:

Het is pyridyl, pyridazinyl, pyrazinyl, thiadiazolyl, benzoxazolyl,1,2,4-triazinyl, 1,3,5-triazinyl, pyrimidinyl or quinoxalinyl, each ofwhich may be optionally substituted with 1 to 3 substituents selectedfrom halo, trifluoromethyl, C₁₋₄alkyl, C₁₋₄alkoxy or hydroxy;

A is a direct bond, O, NH or NMe;

Y is O, S, NH or NMc;

Alk is C₁₋₆ alkylene; and

R¹¹ is OR¹⁰ or SR¹⁰, where R¹⁰ is C₁₋₄alkyl.

Examples of specific compounds within the scope of the present inventionare shown in Tables 1 and 5 below.

TABLE 1

Position of Compd linkage to X No. Heterocycle benz-azole ring GroupY-Substituent 1 6-Me-3-Pyridazinyl 6 O Methyl 2 6-Me-3-Pyridazinyl 5 OMethyl 3 6-Me-3-Pyridazinyl 6 O Ethyl 4 6-Me-3-Pyridazinyl 6 OMethylthio 5 6-Me-3-Pyridazinyl 6 O Ethoxy 6 6-Cl-3-Pyridazinyl 6 OMethylthio 7 6-Me-3-Pyridazinyl 6 O Ethylthio 8 6-Cl-3-Pyridazinyl 6 OEthylthio 9 5-Methyl-1,3,4-Thiadiazol- 6 O Ethylthio yl 105-Methyl-1,3,4-Thiadiazol- 6 O Ethoxy yl 11 6-Me-3-Pyridazinyl 6 On-Propoxy 12 6-Me-3-Pyridazinyl 6 O Methoxy 13 6-Cl-3-Pyridazinyl 6 OEthoxy 14 6-Me-3-Pyridazinyl 6 S Methoxy 15 6-Me-3-Pyridazinyl 6 SEthoxy 16 6-Me-3-Pyridazinyl 5/6 NMe Ethylthio 19 6-Me-3-Pyridazinyl 5 SEthylthio 20 6-Me-3-Pyridazinyl 5 S n-Propoxy 21 6-Me-3-Pyridazinyl 5 SEthoxy 22 6-Me-3-Pyridazinyl 5 O Ethylthio 23 6-Me-3-Pyridazinyl 5 OEthoxy 24 6-Me-3-Pyridazinyl 6 S n-Propylamino 25 6-Me-3-Pyridazinyl 5NH Ethylthio 26 6-Me-3-Pyridazinyl 6 O n-Butyl 27 6-Me-3-Pyridazinyl 6 On-Propyl 28 5,6-Me₂-3-Pyridazinyl 6 O Ethoxy 293-Me-1,2,4-Thiadiazol-5-yl 6 O Ethoxy 30 5,6-Me₂-1,2,4-Triazin-3-yl 6 OEthoxy 31 1-Me-Tetrazol-5-yl 6 O Ethoxy 32 6-Cl-5-Me-3-Pyridazinyl 6 OEthoxy 33 5-Me-3-Pyridazinyl 6 O Ethoxy

TABLE 2

Compound Number Alkylene chain length n Y Substituent 17 3 Ethylthio 183 Ethoxy 34 5 Ethoxy

TABLE 3

Com- Alkylene pound R chain Number Substituent Group A length n Atom XGroup Y 35 Methyl CH 2 O Ethoxy 36 Methyl CH 2 O Ethyl 37 Chloro CH 2 OEthoxy 38 Methyl CH 2 O n-Propoxy 39 Methyl CH 2 O n-Propyl 40 Methyl CH2 S Ethoxy 41 Chloro CH 3 O Ethoxy 42 Methyl N 2 O Ethoxy

TABLE 4

Compound Number X Substituent Y Substituent 43 Ethoxy H 44 Chloro Chloro45 Ethoxy Ethoxy 46 H Ethoxy

TABLE 5 Compound Number Structure 47

48

49

50

51

52

53

54

55

56

57

58

The compounds of the present invention may be prepared using methodsthose described in the prior art. For example, compounds in which theHet formula (a-1) may be prepared using methodology analogous to theprocesses U.S. Pat. Nos. 4,992,433, 5,112,825 and 5,100,893. Similarly,compounds is (a-2), (a-3), (a-4), (a-5) or (a-6) may be prepared usingmethodology similar to that described in U.S. Pat. No. 5,070,090 andAustralian Patent No. 629172, and compounds in which Het is (a-7) or(a-8) may be prepared in accordance with methodology similar to thatdescribed in U.S. Pat. No. 5,364,865.

In one method the compounds of the present invention are prepared via anintermediate of formula XI:

where A, Alk, W, Ar, X¹, X², X³ and B are as described above.

This intermediate may be prepared using methodology similar to thatdescribed in U.S. Pat. No. 5,231,184. In one example intermediates offormula XI, when W is O, are prepared by the reaction of compounds ofthe formula P-A-Alk-OH or P-A-Alk-L with hydroxy aromatic compounds offormula XII.

where Ar, X¹, X², X³ and B are as defined above, P is H or a protectinggroup, and L is a leaving group. Removal of the protecting group P inthe reaction product affords the reactive intermediates of formula XI.

Examples of suitable protecting groups P in compounds of formulaP-A-Alk-OH or P-A-Alk-L include benzyl or acyl moieties which can beintroduced and removed by standard methods (see, “Protective Groups inOrganic Synthesis”, Theodora Green, Wiley Interscience, 1981).

The intermediate of formula XI may be reacted with a compound of formulaHet-L, where Het is as defined above and L is a suitable leaving groupto afford a compound of formula I. Where this reaction is anN-alkylation reaction, it can be conducted using procedures known to theart, such as under the conditions described in U.S. Pat. No. 5,231,184for performing analogous N-alkylations. In performing the reactiondescribed above it may be necessary to protect one or more substituentson groups such as X¹, X², X³ or B.

Some of the intermediates of formula XI and XII are novel and representa further aspect of the present invention.

Examples of suitable leaving groups include halogen, such as fluoro,chloro, bromo and iodo, and halogen-like groups such asp-toluenesulphonyloxy and methanesulphonyloxy.

An additional method of preparing certain compounds of the invention offormula Ia (Compounds for formula I where W═O) involves condensing acompound of formula XIII with a suitable precursor of formula XII:

using Mitsunobu Reaction conditions (see Chemical Syntheses, Vol. 42, p335, 1992) and where Het, A, Alk, X¹, X², X³ and B are as defined forformula I.

Intermediates of formula XII may often be prepared from protected formsof the hydroxy compound. For example compounds of formula XII whereinX¹-X³ are CH (hereinafter referred to as compounds of formula (XIIa))can be made from the corresponding compounds which have an alkoxy orbenzyloxy substituent which can be converted to OH by routinedeprotection reagents including HBr or BBr₃.

The chemical literature contains many references to the preparation ofcompounds of formula (XIIb) including, for example, U.S. Pat. No.5,919,807 and J. Org. Chem., 61, 3289 (1996). Compounds of formula(XIIb) can generally be prepared from the corresponding compounds(XIIc), which have a leaving group L available for displacement by R¹¹when R¹¹ is OR¹⁰, SR¹⁰ or NR⁹R¹⁰. There are several references in theliterature to the preparation of examples of compounds of generalformula (XIIc), for example in U.S. Pat. Nos. 5,919,807 and 5,747,498and J. Med. Chem., 24, 93 (1981).

Several references, including U.S. Pat. Nos. 5,112,825 and 5,242,924,describe methods for the preparation of various compounds of formulaXIII.

The compounds of the present invention are useful in the prevention ortreatment of picomoviral infections in mammals, particularly humans.

Accordingly, in a further aspect the invention provides a method for thetreatment or prophylaxis of a picomaviral infection in a mammalincluding the step of administering an effective amount of a compound offormula I.

The picornavirus infection may be caused by any virus of the familyPicornaviridae. Representative family members include humanrhinoviruses, polioviruses, enteroviruses including coxsackieviruses andechoviruses, hepatovirus, cardioviruses, apthovirus, hepatitis A andother picornaviruses not yet assigned to a particular genus, includingone or more of the serotypes of these viruses. Preferably the inventionis used in the prevention or treatment of infection caused by one ormore serotypes of rhinovirus.

Without wishing to be limited by theory, it is believed that theheteroatoms in the fused heterocyclic moiety of the compound of formulaI may be involved in hydrogen bonding with an asparagine residuegenerally present near the opening of the hydrophobic pocket, and thatthis interaction enhances the binding of the compounds in the capsidpocket, relative to the prior art compounds. It is further believed thatthe fused heterocyclic moiety may be more resistant to hydrolysis andesterase activity than the ester bond of pirodavir, and that this mayallow more flexibility in the methods of administration of the compoundto the site of activity, than available for readily hydrolysablepirodavir. In particular it may allow oral administration of thecompounds or reduce metabolism in the nasal mucosa following topicaladministration.

The salts of the compound of formula I are preferably pharmaceuticallyacceptable, but it will be appreciated that non-pharmaceuticallyacceptable salts also fall within the scope of the present invention,since these are useful as intermediates in the preparation ofpharmaceutically acceptable salts. The pharmaceutically acceptable saltsmay include conventional non-toxic salts or quartenary ammonium salts ofthese compounds, which may be formed, e.g., from organic or inorganicacids or bases. Examples of such acid addition salts include, but arenot limited to, those formed with pharmaceutically acceptable acids suchas acetic, propionic, citric, lactic, methanesulphonic,toluenesulphonic, benzenesulphonic, salicyclic, ascorbic, hydrochloric,orthophosphoric, sulphuric and hydrobromic acids. Base salts includes,but is not limited to, those formed with pharmaceutically acceptablecations, such as sodium, potassium, lithium, calcium magnesium, ammoniumand alkylammonium. Also, basic nitrogen-containing groups may bequaternised with such agents as lower alkyl halides, such as methyl,ethyl, propyl, and butyl chlorides, bromides and iodides; dialkylsulfates like dimethyl and diethyl sulfate; and others.

The compounds of the invention may be in crystalline form or as solvates(e.g., hydrates) and it is intended that both forms are within the scopeof the present invention. Methods of solvation are generally knownwithin the art.

Pharmaceutically acceptable derivatives may include any pharmaceuticallyacceptable salt, hydrate or any other compound or prodrug which, uponadministration to a subject, is capable of providing (directly orindirectly) a compound of formula I or an antivirally active metaboliteor residue thereof.

Any compound that is a prodrug of a compound of formula I is within thescope and spirit of the invention. The term “pro-drug” is used in itsbroadest sense and encompasses those derivatives that are converted invivo to the compounds of the invention. Such derivatives would readilyoccur to those skilled in the art, and include, for example, compoundswhere a free hydroxy group is converted into an ester derivative or aring nitrogen atom is converted to an N-oxide. Examples of esterderivatives include alkyl esters, phosphate esters and those formed fromamino acids, preferably valine.

It will be appreciated that some derivatives of the compound of formulaI may have an asymmetric center, and therefore are capable of existingin more than one stereoisomeric form. The invention extends to each ofthese forms individually and to mixtures thereof, including racemates.The isomers may be separated conventionally by chromatographic methodsor using a resolving agent. Alternatively the individual isomers may beprepared by asymmetric synthesis using chiral intermediates.

The invention also provides the use of a compound of formula I in themanufacture of a medicament for the treatment or prophylaxis ofpicornavirus infection.

While it is possible that, for use in therapy, a compound of theinvention may be administered as the neat chemical, it is preferable topresent the active ingredient as a pharmaceutical formulation.

In view of the general lipophilic nature of the compounds, they areparticularly suitable to oral forms of administration; however, otherforms of administration are also envisaged.

The invention thus further provides pharmaceutical formulationscomprising a compound of the invention or a pharmaceutically acceptablesalt or derivative thereof together with one or more pharmaceuticallyacceptable carriers therefor and, optionally, other therapeutic and/orprophylactic ingredients. The carrier(s) must be acceptable in the senseof being compatible with the other ingredients of the formulation andnot deleterious to the recipient thereof.

The compounds of this invention may also be useful in combination withknown anti-viral or anti-retroviral agents or other pharmaceuticals usedin the treatment of viral infections. Representative examples of theseadditional pharmaceuticals include immunomodulators, immunostimulants,antibiotics and anti-inflammatory agents. Exemplary anti-viral agentsinclude zanamivir, rimantidine, amantidine, ribavirin, AZT, 3TC, (−)FTC, acyclovir, famciclovir, penciclovir, ddI, ddC, ganciclovir,saquanivir, loviride, other non-nucleotide reverse transcriptase (RT)inhibitors and protease inhibitors, antiviral and antireceptorantibodies and receptor analogues, such as ICAM-1. Exemplaryimmunomodulators and immunostimulants include various interleukins,cytokines and antibody preparations. Exemplary antibiotics includeantifungal agents and antibacterial agents. Exemplary anti-inflammatoryagents include glucocorticoids and non-steroidal anti-inflammatorycompounds.

Pharmaceutical formulations include those suitable for oral, rectal,nasal, topical (including buccal and sub-lingual), vaginal or parenteral(including intramuscular, subcutaneous and intravenous) administrationor in a form suitable for administration by inhalation or insufflation.The compounds of the invention, together with a conventional adjuvant,carrier, or diluent, may thus be placed into the form of pharmaceuticalcompositions and unit dosages thereof, and in such form may be employedas solids, such as tablets or filled capsules, or liquids such assolutions, suspensions, emulsions, elixirs, or capsules filled with thesame, all for oral use, in the form of suppositories for rectaladministration; or in the form of sterile injectable solutions forparenteral (including subcutaneous) use. Such pharmaceuticalcompositions and unit dosage forms thereof may comprise conventionalingredients in conventional proportions, with or without additionalactive compounds or principles, and such unit dosage forms may containany suitable effective amount of the active ingredient commensurate withthe intended daily dosage range to be employed. Formulations containingten (10) milligrams of active ingredient or, more broadly, 0.1 to twohundred (200) milligrams, per tablet, are accordingly suitablerepresentative unit dosage forms. The compounds of the present inventioncan be administered in a wide variety of oral and parenteral dosageforms. It will be obvious to those skilled in the art that the followingdosage forms may comprise, as the active component, either a compound ofthe invention or a pharmaceutically acceptable salt of a compound of theinvention.

For preparing pharmaceutical compositions from the compounds of thepresent invention, pharmaceutically acceptable carriers can be eithersolid or liquid. Solid form preparations include powders, tablets,pills, capsules, cachets, suppositories, and dispersible granules. Asolid carrier can be one or more substances which may also act asdiluents, flavoring agents, solubilizers, lubricants, suspending agents,binders, preservatives, tablet disintegrating agents, or anencapsulating material.

In powders, the carrier is a finely divided solid which is in a mixturewith the finely divided active component.

In tablets, the active component is mixed with the carrier having thenecessary binding capacity in suitable proportions and compacted in theshape and size desired.

The powders and tablets preferably contain from five or ten to aboutseventy percent of the active compound. Suitable carriers are magnesiumcarbonate, magnesium stearate, talc, sugar, lactose, pectin, dextrin,starch, gelatin, tragacanth, methylcellulose, sodiumcarboxymethylcellulose, a low melting wax, cocoa butter, and the like.The term “preparation” is intended to include the formulation of theactive compound with encapsulating material as carrier providing acapsule in which the active component, with or without carriers, issurrounded by a carrier, which is thus in association with it.Similarly, cachets and lozenges are included. Tablets, powders,capsules, pills, cachets, and lozenges can be used as solid formssuitable for oral administration.

For preparing suppositories, a low melting wax, such as admixture offatty acid glycerides or cocoa butter, is first melted and the activecomponent is dispersed homogeneously therein, as by stirring. The moltenhomogenous mixture is then poured into convenient sized molds, allowedto cool, and thereby to solidify.

Formulations suitable for vaginal administration may be presented aspessaries, tampons, creams, gels, pastes, foams or sprays containing inaddition to the active ingredient such carriers as are known in the artto be appropriate.

Liquid form preparations include solutions, suspensions, and emulsions,for example, water or water-propylene glycol solutions. For example,parenteral injection liquid preparations can be formulated as solutionsin aqueous polyethylene glycol solution.

The compounds according to the present invention may thus be formulatedfor parenteral administration (e.g., by injection, for example bolusinjection or continuous infusion) and may be presented in unit dose formin ampoules, pre-filled syringes, small volume infusion or in multi-dosecontainers with an added preservative. The compositions may take suchforms as suspensions, solutions, or emulsions in oily or aqueousvehicles, and may contain formulatory agents such as suspending,stabilizing and/or dispersing agents. Alternatively, the activeingredient may be in powder form, obtained by aseptic isolation ofsterile solid or by lyophilization from solution, for constitution witha suitable vehicle, e.g., sterile, pyrogen-free water, before use.

Aqueous solutions suitable for oral use can be prepared by dissolvingthe active component in water and adding suitable colorants, flavors,stabilizing and thickening agents, as desired.

Aqueous suspensions suitable for oral use can be made by dispersing thefinely divided active component in water with viscous material, such asnatural or synthetic gums, resins, methylcellulose, sodiumcarboxymethylcellulose, or other well known suspending agents.

Also included are solid form preparations that are intended to beconverted, shortly before use, to liquid form preparations for oraladministration. Such liquid forms include solutions, suspensions, andemulsions. These preparations may contain, in addition to the activecomponent, colorants, flavors, stabilizers, buffers, artificial andnatural sweeteners, dispersants, thickeners, solubilizing agents, andthe like.

For topical administration to the epidermis, the compounds according tothe invention may be formulated as ointments, creams or lotions, or as atransdermal patch. Ointments and creams may, for example, be formulatedwith an aqueous or oily base with the addition of suitable thickeningand/or gelling agents. Lotions may be formulated with an aqueous or oilybase and will in general also contain one or more emulsifying agents,stabilizing agents, dispersing agents, suspending agents, thickeningagents, or coloring agents.

Formulations suitable for topical administration in the mouth includelozenges comprising the active agent in a flavored base, usually sucroseand acacia or tragacanth; pastilles comprising the active ingredient inan inert base such as gelatin and glycerin or sucrose and acacia; andmouthwashes comprising the active ingredient in a suitable liquidcarrier.

Solutions or suspensions are applied directly to the nasal cavity byconventional means, for example with a dropper, pipette or spray. Theformulations may be provided in single or multidose form. In the lattercase of a dropper or pipette, this may be achieved by the patientadministering an appropriate predetermined volume of the solution orsuspension. In the case of a spray, this may be achieved for example bymeans of a metering atomizing spray pump. To improve nasal delivery andretention, the compounds according to the invention may be encapsulatedwith cyclodextrins, or formulated with their agents expected to enhancedelivery and retention in the nasal mucosa.

Administration to the respiratory tract may also be achieved by means ofan aerosol formulation in which the active ingredient is provided in apressurized pack with a suitable propellant such as a chlorofluorocarbon(CFC), for example dichlorodifluoromethane, trichlorofluoromethane, ordichlorotetrafluoroethane, carbon dioxide, or other suitable gas. Theaerosol may conveniently also contain a surfactant such as lecithin. Thedose of drug may be controlled by provision of a metered valve.

Alternatively the active ingredients may be provided in the form of adry powder, for example a powder mix of the compound in a suitablepowder base such as lactose, starch, starch derivatives such ashydroxypropylmethyl cellulose and polyvinylpyrrolidone (PVP).

Conveniently the powder carrier will form a gel in the nasal cavity. Thepowder composition may be presented in unit dose form for example incapsules or cartridges of, e.g., gelatin, or blister packs from whichthe powder may be administered by means of an inhaler.

In formulations intended for administration to the respiratory tract,including intranasal formulations, the compound will generally have asmall particle size, for example of the order of 1 to 10 microns orless. Such a particle size may be obtained by means known in the art,for example by micronization.

When desired, formulations adapted to give sustained release of theactive ingredient may be employed.

The pharmaceutical preparations are preferably in unit dosage forms. Insuch form, the preparation is subdivided into unit doses containingappropriate quantities of the active component. The unit dosage form canbe a packaged preparation, the package containing discrete quantities ofpreparation, such as packeted tablets, capsules, and powders in vials orampoules. Also, the unit dosage form can be a capsule, tablet, cachet,or lozenge itself, or it can be the appropriate number of any of thesein packaged form.

Liquids or powders for intranasal administration, tablets or capsulesfor oral administration and liquids for intravenous administration arepreferred compositions.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with reference to the followingexamples which illustrate some preferred aspects of the presentinvention. However, it is to be understood that the particularity of thefollowing description of the invention is not to supersede thegenerality of the preceding description of the invention.

EXAMPLES Example 1 Preparation of6-{2-[1-(6-Methyl-3-pyridazinyl)-4-piperidinyl]ethoxy}-2-methylthiobenzoxazole(Compound 4 from Table 1) (a) Preparation of2-mercapto-6-hydroxybenzoxazole (see also J. Org. Chem., 19, 758)

A mixture of a minoresorcinol hydrochloride (1.1 g), potassium ethylxanthate (1.2 g) and potassium carbonate (1.0 g) was dissolved inethanol/water (1:1, 20 ml) and (under an argon balloon) heated underreflux for 3 hours. The pale yellow solution was cooled to RT and thenacetic acid (2 ml) was added to make the solution slightly acidic (gasevolution). A cream precipitate soon formed and the sealed flask waskept in the fridge overnight. The cream solid was collected byfiltration and the damp product (0.9 g) was used immediately in the nextstep.

(b) Preparation of 6-hydroxy-2-methylthiobenzoxazole

A mixture of 6-hydroxy-2-mercaptobenzoxazole (165 mg), sodiumbicarbonate (84 mg) and dimethyl sulfate (94 μl) was dissolved in water(2 ml) with stirring and under an argon atmosphere. The reaction mixturewas stirred at RT overnight and HPLC showed that all starting materialwas gone. The reaction mixture was evaporated to dryness to give a darkbrown solid (one can also extract the reaction mixture with chloroformto give the crude product). Chromatography on silica gel using 10% ethylacetate/hexane gave the pure product as a near-white crystalline solid(45 mg, 25%).

(c) Preparation of2-Methylthio-6-[N-(6-methyl-3-pyridazinyl)piperidinyl-4-ethoxy]benzoxazole(Compound 4)

A mixture of 6-hydroxy-2-methylthiobenzoxazole (100 mg),3-[4-(2-chloroethyl)-1-piperidinyl]-6-methylpyridazine (130 mg) andpotassium carbonate (100 mg) was heated and stirred in DMF (3 ml) at90-100° under argon for 20 hr. Tlc showed that the reaction wasvirtually complete and the DMF was removed under reduced pressure andthe residue was partitioned between water and chloroform. The chloroformextracts were evaporated and the residue was chromatographed onsilica/chloroform to give the product as a pale cream solid (110 mg,50%). The ¹H nmr spectrum is summarized in Table 6 below.

Example 2 Preparation of2-Ethoxy-6-{2-[N-(6-methyl-3-pyridazinyl)piperidinyl]-4-ethoxy}benzoxazole(Compound No 5)

Sodium metal (100 mg) was dissolved in ethanol (5 ml) and the solutionwas added to a solution of the methylthiobenzoxazole (compound No. 4)(74 mg) in THF (2 ml). The resultant solution was stirred at RT for 24hr when hplc indicated that all starting material had disappeared. Thereaction mixture was evaporated to dryness and the residue waspartitioned between water and dichloromethane. The crude organic productwas purified by chromatography on silica/CH₂Cl₂ to give Compound No. 5as a pale cream solid (46 mg). The ¹H nmr and MS data are recorded inTable 6 below.

Example 3

Compounds No 1, 2, 3, 6, 7, 8, 9, 17, 19, 22, 25, 26, 27 were preparedby reacting the appropriate Het-A-Alk-Cl or Het-A-Alk-OH with therequired 2-substituted 5- or 6-hydroxybenz-azole (benzoxazole,benzothiazole or benzimidazole) following similar conditions to thosedescribed in Example 1 part (c). The ¹H nmr and/or MS data are recordedin Table 6 below.

Example 4

The 2-alkoxybenz-azole derivatives, Compounds No 10, 11, 12, 13, 14, 15,18, 20, 21, 23 were prepared from the corresponding 2-methylthio or2-ethylthiobenzoxazole or benzothiazole by reaction with the appropriatesodium alkoxide following essentially the same conditions as describedin Example 2. The ¹H nmr and/or MS data are recorded in Table 6 below.

Example 5 Preparation of a mixture of2-Ethylthio-3-Methyl-6-{2-[N-(6-methyl-3-pyridazinyl)piperidinyl]-4-ethoxy}benzimidazoleand2-Ethylthio-3-Methyl-5-{2-[N-(6-methyl-3-pyridazinyl)piperidinyl]-4-ethoxy}benzimidazole(Compound No 16)

Methylation of 2-ethylthio-5-hydroxybenzimidazole gave an approximately1:1 mixture of 2-ethylthio-3-methyl-5-hydroxybenzimidazole and2-ethylthio-3-methyl-6-hydroxybenzimidazole which could not be easilyseparated. Reaction of this mixture of hydroxy compounds with3-[4-(2-chloroethyl)-1-piperidinyl]-6-methylpyridazine, following themethod described in Example 1, gave a 1:1 mixture of isomeric products(Compound No 16).

Example 6 Preparation of6-{2-[1-(6-Methyl-3-pyridazinyl)-4-piperidinyl]ethoxy}-3-ethoxy-1,2-benzisoxazole(Compound 35 from Table 3) (a) Preparation of2-hydroxy-4-methoxybenzohydroxamic acid according to literatureprocedure Chem. Ber. 100, 954-960 (1967)

An hydroxylamine solution was prepared by addition of aqueous sodiumhydroxide (393 mg, 9.82 mmol)/water (1.6 ml) to a stirred solution ofhydroxylamine hydrochloride (292 mg, 4.21 mmol) in water (3.5 ml).Immediately slowly added a solution of methyl2-hydroxy-4-methoxybenzoate (511 mg, 2.81 mmol) in 1,4-dioxane (1.5 ml).The resulting reaction mixture was stirred at room temperature for 18hours, under an argon atmosphere. The reaction mixture was concentratedon a rotary evaporator to half the original volume, and the productprecipitated by addition of concentrated hydrochloric acid, keepingflask cool in an ice bath. Filtered the suspension to give2-hydroxy-4-methoxybenzohydroxamic acid (476 mg, 92%) as a pale brownsolid.

¹H nmr spectrum (CDCl₃) δ (ppm): 3.72 (s, 3H); 6.36 (m, 2H); 7.41 (d,1H).

(b) Preparation of 3-hydroxy-6-methoxy-1,2-benzisoxazole

A solution of carbonyl diimidazole (1.07 g, 6.57 mmol) in anhydrous THF(8 ml) was added to a stirred boiling solution of the hydroxamic acid(602 mg, 3.29 mmol) in THF (6 ml). The resulting solution was heated atreflux for approx. 8-10 hours, then allowed to cool to room temperatureand stirred overnight under an argon atmosphere. Thin layerchromatography (tlc) (silica; 1:1 hexane/ethyl acetate) showed minimalstarting material and new non polar material. The solution wasevaporated on a rotary evaporator to give an orange colored oil. Water(6 ml) was added, and contents cooled (ice bath) and acidified to pH 2with concentrated hydrochloric acid. The crude, damp3-hydroxy-6-methoxy-1,2-benzisoxazole precipitated as a cream orangesolid (645 mg).

¹H nmr spectrum (CDCl₃) δ (ppm): 3.82 (s, 3H); 6.73 (fd, 1H); 6.80 (dd,1H); 7.52 (d, 1H).

LCMS (ESI) 166 (M+1)⁺

(c) Preparation of 3-ethoxy-6-methoxy-1,2-benzisoxazole

Benzisoxazole from part (b) (193 mg, 1.17 mmol), ethanol (75 μl, 1.29mmol) and triphenylphosphine (460 mg, 1.75 mmol) were dissolved inanhydrous THF (4 ml) and cooled (0°). Diisopropylazodicarboxylate (345μl, 1.75 mmol) was added slowly and after 10-15 min the reaction flaskwas removed from the ice bath and the reaction mixture was stirred atroom temperature overnight under an argon atmosphere. The solution wasevaporated to dryness and the residue pre-absorbed onto silica, andchromatographed on silica (19 g); eluent:hexane (300 ml), 10-30% ethylacetate/hexane to give 3-ethoxy-6-methoxy-1,2-benzisoxazole (101 mg,44%) as white crystals.

¹H nmr spectrum (CDCl₃) δ (ppm): 1.50 (t, 3H); 3.87 (s, 3H); 4.47 (q,2H); 6.86 (m, 2H), 7.47 (d, 1H).

LCMS (ESI) 194 (M+1)⁺

(d) Preparation of 3-ethoxy-6-hydroxy-1,2-benzisoxazole

Boron tribromide (1.0M solution in dichloromethane; 1.39 ml, 1.39 mmol)was added to a stirred, −78° cooled solution of benzisoxazole from part(c) (179 mg, 928 μmol) in dichloromethane (4 ml) under an argonatmosphere. The reaction mixture was gradually warmed to roomtemperature over approx. 2 hours, and stirred overnight. Tlc (silica,2:1 hexane/ethyl acetate) showed new polar material as well as unreactedstarting material. The reaction was worked up by adding water (5 ml) andice. The aqueous phase was neutralized by addition of saturated NaHCO₃solution, and saturated with NaCl. The aqueous phase was extracted intodichloromethane (3×60 ml), then the organic extracts combined and washedwith brine (10 ml) and dried (NaSO₄). The product was purified bychromatography on silica (18 g; eluent 2.5%, 5%, then 15% ethylacetate/hexane). The first compound to elute was unreacted3-ethoxy-6-methoxy-1,2-benzisoxazole, (46 mg), followed by3-ethoxy-6-hydroxy-1,2-benzisoxazole 108 mg (65%).

¹H nmr spectrum (CDCl₃) δ (Ppm): 1.45 (t, 3H); 4.40 (q, 2H); 6.74 (m,2H); 7.38 (m, 1H).

LCMS (ESI) 180 (M+1)⁺

(e) Preparation of Compound 35

A mixture of 2-[-1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethanol (42mg, 188 μmol), benzisoxazole from part (d) (28 mg, 156 μmol) andpolymer-supported triphenylphosphine (145 mg, 234 μmol) in anhydrous THF(3 ml) was cooled (0°) and stirred under an argon atmosphere. Neatdiisopropylazodicarboxylate (46 μml, 234 μmol) was added slowly and thereaction mixture was allowed to warm to room temperature and stirovernight. The reaction mixture was filtered, then pre-adsorbed ontosilica and chromatographed on silica (approx. 5 g); using firstly 2:1hexane/ethyl acetate as eluent, then gradually increased to 70% ethylacetate/hexane to afford Compound 35 (44 mg; 73%) as a white powder. The¹H nmr and MS data are recorded in Table 6 below.

Example 7

Compounds No 36, 37, 38, 39, 40, 41, 42, 49, 50, 56 and 57 were preparedby reacting the appropriate Het-A-Alk-Cl or Het-A-Alk-OH with therequired 3-substituted 6-hydroxy-1,2-benzisoxazole (or1,2-benzisothiazole) following similar conditions to those described inExample 6. The ¹H nmr and/or MS data are recorded in Table 6 below.

Example 8

The n-propylaminobenzothiazole derivative, Compound No 24, was preparedfrom the corresponding 2-methoxy-benzothiazole (Compound 14) by heatingwith excess n-propylamine. The ¹H nmr and/or MS data are recorded inTable 6 below.

Example 9 Preparation of2-Ethoxy-6-{2-[N-(5,6-dimethyl-3-pyridazinyl)piperidinyl]-4-ethoxy}benzoxazole(Compound No 28) (a) Preparation of 2-ethoxy-6-hydroxybenzoxazole

A mixture of equivalent amounts of 4-aminoresorcinol hydrochloride andanhydrous sodium acetate in anhydrous ethanol was stirred for 16 hoursat room temperature with a slight excess of tetraethyl orthocarbonate togive 2-ethoxy-6-hydroxybenzoxazole in 60% yield.

(b) Reaction of 2-ethoxy-6-hydroxybenzoxazole with2-[-1-(5,6-dimethyl-3-pyridazinyl)-4-piperidinyl]ethanol was carried outusing a Mitsunobu coupling and similar conditions to those described inExample 6 part (e). The ¹H nmr and/or MS data for Compound 28 arerecorded in Table 6 below.

Example 10

Compounds No 29, 30, 31, 32, 33, 34, 47 and 48 were prepared by reactingthe appropriate Het-A-Alk-Cl or Het-A-Alk-OH with2-ethoxy-6-hydroxybenzoxazole following similar conditions to thosedescribed in Example 1, part (c) or Example 6 part (e). The ¹H nmrand/or MS data are recorded in Table 6 below.

Example 11 Preparation of6-{2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethoxy}-4-ethoxy-cinnoline(Compound 53 from Table 5) (a) Preparation of4-chloro-6-methoxycinnoline

6-Methoxy-4-hydroxycinnoline (Osborn, A. R. and Schofield, K. J. Chem.Soc., 1955, 2100) was prepared from 2-amino-5-methoxyacetophenone bydiazotisation.

Phosphorous oxychloride (5 ml) was added to a mix of dimethylaniline(157 mg, 1.3 mmol) and 6-methoxy-4-hydroxycinnoline (208 mg, 1.2 mmol).The reaction was heated at reflux for 15 min, then cooled andconcentrated under vacuum. The residue was partitioned betweenchloroform (100 ml) and water (30 ml), then the organic layer was washedwith brine and dried (Na₂SO₄). Chromatography of the residue adsorbedonto silica gel (3 g) on silica gel (15 g) eluent CH₂Cl₂ to 10%Ethylacetate/CH₂Cl₂ gave 6-methoxy-4-chlorocinnoline (135 mg, 0.7 mmol)in 59% yield as white yellow solid. δ_(H) (CDCl₃)=4.03 (s, 3H); 7.28 (d,1H); 7.51 (dd, 1H); 8.41 (d, 1H) and 9.22 (br s, 1H). MS (ESI) (M+H)⁺195.

(b) Preparation of 4-chloro-6-hydroxycinnoline

A solution of 6-methoxy-4-chlorocinnoline (135 mg, 0.7 mmol) in toluene(7 ml) was added to a stirred suspension of aluminium trichloride (231mg, 1.73 mmol) in toluene (7 ml) and the red brown suspension wasrefluxed for 1 hr. The solvent was removed under vacuum and the residuewas partitioned between water (20 ml) and 10% ethanol/chloroform (2×100ml). The organic layer was washed with brine and dried (Na₂SO₄). Removalof the solvent under vacuum gave 6-hydroxy-4-chlorocinnoline (154 mg) asa single component by TLC (1:1 ethylacetate/hexanes). δ_(H) (CD₃OD)=7.33(d, 1H); 7.56 (dd, 1H); 8.32 (d, 1H) and 9.15 (br s 1H). MS (ESI) (M+H)⁺181.

(c) Preparation of6-{2-[(1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethoxy)}-4-chlorocinnoline

A solution of DIAD (42 mg, 0.21 mmol) in THF (0.4 ml) was added slowlyto a suspension containing 6-hydroxy-4-chlorocinnoline (30 mg, 0.17mmol), triphenylphosphine (65 mg, 0.25 mmol) and1-(6-methyl-3-pyridazinyl)-4-(2-hydroxyethyl)-piperidine (40 mg, 0.18mmol) in THF (5 ml) and the suspension cleared. The reaction was left tostir overnight, then the reaction was adsorbed onto silica (1.5 g) andchromatography on silica gel (8 g) eluent ethylacetate gave the product(50 mg, 0.13 mmol) in 72% yield. ¹H nmr δ_(H) (CD₃OD)=1.35 (m, 2H); 1.9(m, 5H); 2.46 (s, 3H); 2.95 (m, 2H); 4.34 (m, 4H); 7.19 (d, 1H); 7.26(d, 1H); 7.42 (d, 1H); 7.64 (dd, 1H); 8.34 (d 1H) and 9.24 (br s 1H).

MS (ESI) (M+H)⁺ 384.

(d) Preparation of Compound No 53

A solution of sodium ethoxide (0.3 mmol) in ethanol (0.15 ml) was addeddropwise to a solution of the above (part c) 4-chlorocinnoline (23 mg,60 μmol) in dry ethanol (3 ml) and the reaction was allowed to stir for2 hr. The reaction was quenched with saturated ammonium chloride/brine(1 ml) and solvents removed under vacuum. The residue was partitionedbetween brine (5 ml) and 5% ethanol/ethylacetate (2×30 ml), dried(Na₂SO₄) and adsorbed onto silica (1 g) under vacuum. Chromatography onsilica gel (8 g) eluent 5% methanol/ethylacetate gave Compound No 53 (15mg, 38 mol) in 63% yield.

Example 12 Preparation of7-{2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethoxy}-4-ethoxy-cinnoline(Compound 52 from Table 5)

4-Hydroxy-7-methoxy-cinnoline (Osborn, A. R. and Schofield, K. J. Chem.Soc. (1955) 2100) was prepared following a similar method to thatdescribed in Example 11 for the 6-isomer. This compound was converted toCompound 52 in a similar manner to that described in Example 11 for the6-isomer. The ¹H nmr and MS data are recorded in Table 6 below

Example 13 Preparation of7-{2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethoxy}-4-ethoxy-quinazoline(Compound 51 from Table 5) (a) Synthesis of 7-nitroquinazolin-4-one

A mixture of 4-nitroanthranilic acid (2.17 g, 11.91 mmol) and formamide(1.5 mL, 38.43 mmol) was heated at 165° C. for 4 hours. The warmreaction mixture was poured into ice/water (30 mL) and the resultingprecipitate was collected via filtration, to give an orange solid (2.16g, 95% yield) which was dried over P₂O₅. This was used without furtherpurification.

¹H nmr; 8.24 (d, 1H), 8.32 (s, 1H), 8.34 (s, 1H), 8.35 (d, 1H).

(b) Synthesis of 7-Aminoquinazolin-4-one

Pd/C (100 mg) was added as a single portion to a degassed and flushed(3×Ar) suspension of 7-nitroquinazolin-4-one (1.15 g, 6.02 mmol) inmethanol (150 mL). The resulting black mixture was degassed, flushedwith hydrogen and allowed to stir for 4 hours. The mixture was filteredthrough celite, washed well with methanol, and the filtrate concentratedto give a tanned solid. This was purified by column chromatography(silica) using 10% methanol/ethyl acetate as the eluent. Combinedfractions gave a beige solid (949 mg, 98% yield).

¹H nmr; 6.68 (s, 1H), 6.87 (d, 1H), 7.73 (d, 1H), 7.83 (s, 1H), 11.40(bs, 1H).

(c) Synthesis of 7-Hydroxyquinazolin-4-one

A solution of sodium nitrite (1.40 g, 20.32 mmol) in water (17 mL) wasadded dropwise to a cooled suspension of 7-aminoquinazolin-4-one (712mg, 4.42 mmol) in sulfuric acid/water (4.4 mL, 18 mL), keeping thetemperature at approx. 0° C. The mixture was stirred at room temperaturefor 2 hours, diluted with water (15 mL) and heated at reflux for 15minutes. The cooled mixture was neutralized and the precipitate wascollected via filtration, and purified by column chromatography (silica)using 10% methanol/ethyl acetate as the eluent. The combined fractionsgave an orange solid (541 mg, 76%).

¹H nmr; 6.85-6.91 (m, 2H), 7.87 (s, 1H), 7.92 (s, 1H).

(d) Synthesis of 7-Hydroxy-4-ethoxyquinazoline

A mixture of 7-hydroxyquinazolin-4-one (105 mg, 648 μmol), phosphorousoxychloride (2 ml), and dimethylaniline (85 μl, 671 μmol) was heated atreflux for 15 minutes in an argon atmosphere. The cooled mixture wasconcentrated under vacuum, and kept in an argon atmosphere to avoidhydrolysis. This residue was dissolved in ethanol (anhydrous, 3 mL), anda solution of sodium (283 mg, 12.34 mmol) in ethanol (3 ml) was addeddropwise. The resulting yellow mixture was stirred at room temperatureunder argon for 2 hours, acidified to pH 6 using NaH₂PO₄ and extractedwith ethyl acetate (3×50 mL). The combined extracts were dried (MgSO₄),filtered and concentrated. The white solid (156 mg) was used withoutfurther purification.

¹H nmr; 1.49 (t, 3H), 4.78 (q, 2H), 7.26 (d, 1H), 7.43 (s, 1H), 8.11 (d,1H), 8.83 (s, 1H).

(e) Preparation of Compound No. 51

A mixture of 3-[4-(2-chloroethyl)-1-piperidinyl]-6-methylpyridazine (76mg, 318 μmol), 7-hydroxy-4-ethoxyquinazoline (100 mg, 526 μmol),potassium carbonate (109 mg, 789 μmol) and potassium iodide (53 mg, 319μmol) in DMF (5 mL) was heated at 90° C. overnight in an argonatmosphere. The mixture was concentrated, and the residue partitionedbetween ethyl acetate (100 mL), and water (20 mL). The organic phase wasdried (MgSO₄), filtered, concentrated and purified by columnchromatography (silica), using gradient elution (ethylacetate-methanol/EA). The combined fractions gave a white solid (22 mg,18%). The ¹H nmr data are recorded in Table 6 below.

Example 14

Compounds No 54 and 55 were prepared by reacting3-[4-(2-chloroethyl)-1-piperidinyl]-6-methylpyridazine with theappropriate 6-hydroxyquinazoline following similar conditions to thosedescribed in Example 13, part (e). The ¹H nmr and/or MS data arerecorded in Table 6 below.

Example 15 Preparation of6-{2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethoxy}-2-ethoxy-quinoxaline(Compound 43 from Table 4) (a) Preparation of2-chloro-6-hydroxyquinoxaline

Aluminium trichloride (85 mg, 638 μmol) was added as a single portion toa stirred mixture of 2-chloro-6-methoxyquinoxaline (73 mg, 375 μmol) andanhydrous toluene (3 ml) under an Argon atmosphere. The reaction mixturewas heated at reflux for approx. 1 hr, then allowed to stir overnight atroom temperature. Tlc (silica; 2:1 hexane/ethyl acetate) showed noremaining starting material and new polar material. Water (1 ml) and icewere added and the mixture stirred. The contents were partitionedbetween water (5 ml) and ethyl acetate (100 ml). The aqueous phase wasextracted into ethyl acetate (50 ml), then the organic extracts combinedand washed with water (10 ml), followed by brine (10 ml) and dried(Na₂SO₄). Concentration gave a brown solid, which was pre-adsorbed ontosilica, then chromatographed on silica (9 g); eluent: 20% ethyl acetatein hexane then 25% ethyl acetate in hexane to give2-chloro-6-hydroxyquinoxaline 54 mg (79%).

(b) Preparation of2-chloro-6-{2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethoxy}-quinoxaline

A mixture of 2-chloro-6-hydroxyquinoxaline (52 mg, 288 μmol),3-[-4-(2-chloroethyl)-1-piperidinyl]-6-methylpyridazine (76 mg, 317μmol), potassium iodide (53 mg, 317 μmol) and potassium carbonate (199mg, 1.44 mmol) in anhydrous dimethylformamide (2 ml) was heated at 90°under an Argon atmosphere for 2 days. Tlc (silica; ethyl acetate) showednew polar material. Removal of the solvent under high vacuum and thenchromatography on silica (5 g; eluent: 30% hexane in ethyl acetate) gavethe product as a white solid 68 mg (61%).

(c) Preparation of Compound 43

Sodium (78 mg, 3.39 mmol) was added portionwise to anhydrous ethanol (2ml). The resulting sodium ethoxide solution was added to a stirredsolution of the chloroquinoxaline from part (b) (65 mg, 169 μmol) inanhydrous tetrahydrofuran (2 ml) under an Argon atmosphere. The reactionmixture was heated at reflux for several hours then allowed to stir atroom temperature overnight. The reaction mixture was quenched withsaturated ammonium chloride solution (1 ml), then the contentspartitioned between water (3 ml) and dichloromethane (50 ml). Theaqueous phase was extracted into dichloromethane (50 ml), the organicextracts combined and washed with brine then dried (Na₂SO₄). The crudeproduct was pre-adsorbed onto silica then chromatographed on silica (11g; eluent 2:1 ethyl acetate/hexane) to give Compound 43 as a white solid(57 mg 86%).

Example 16

Compounds No 44, 45 and 46 were prepared by reacting3-[4-(2-chloroethyl)-1-piperidinyl]-6-methylpyridazine or2-[-1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethanol with theappropriate 6-hydroxyquinoxaline following similar conditions to thosedescribed in earlier examples. The ¹H nmr and/or MS data are recorded inTable 6 below.

Example 17

The compounds of the invention which are listed in Tables 1 to 5 weregenerally purified by chromatography on silica gel and were isolated assolids and characterised by ¹H nmr and mass spectroscopy. Forconvenience, the nmr and ms data are recorded in Table 6 below.

TABLE 6 Compound MS data NMR data: Proton Chemical Shift d in ppm No.(ESI) (CDCl₃ unless otherwise noted) 19 415 1.35 (m, 1H), 1.49 (t, 3H),1.80-1.90 (m, 6H), (M + 1)⁺ 2.64 (s, 3H), 2.99 (m, 2H), 3.34 (q, 2H),4.10 (t, 2H), 4.37 (m, 2H), 6.93 (dd, 1H), 7.05 (d, 1H), 7.21 (d, 1H),7.38 (s, 1H), 7.59 (d, 1H). 20 413 1.05 (t, 3H), 1.33 (m, 1H), 1.88 (m,8H), 2.79 (M + 1)⁺ (s, 3H), 3.10 (m, 2H), 4.07 (t, 2H), 4.40 (m, 2H),4.50 (t, 2H), 6.84 (dd, 1H), 7.22 (s, 1H), 7.25 (d, 1H), 7.42 (d, 1H),7.48 (m, 1H) 21 399 1.33 (m, 1H), 1.48 (t, 3H), 1.79 (m, 2H), 1.92 (M +1)⁺ (m, 4H), 2.73 (s, 3H), 3.04 (m, 2H), 4.07 (t, 2H), 4.39 (m, 2H),4.60 (q, 2H), 6.84 (dd, 1H), 7.22 (s, 1H), 7.25 (d, 1H), 7.36 (d, 1H),7.48 (d, 1H) 22 Not 1.35 (m, 1H), 1.49 (t, 3H), 1.80-1.90 (m, 6H),recorded 2.58 (s, 3H), 2.99 (m, 2H), 3.32 (q, 2H), 4.05 (t, 2H), 4.37(m, 2H), 6.85 (dd, 1H), 6.95 (d, 1H), 7.1 (m, 2H), 7.35 (d, 1H). 23 Not1.35 (m, 1H), 1.53 (t, 3H), 1.80-1.90 (m, 6H), recorded 2.58 (s, 3H),2.99 (m, 2H), 4.05 (t, 2H), 4.37 (m, 2H), 4.60 (q, 2H), 6.76 (dd, 1H),6.95 (d, 1H), 7.0-7.1 (m, 2H), 7.15-7.25 (m, 2H). 24 412 1.01 (t, 3H),1.35 (m, 3H), 1.68-1.88 (m, 6H), (M + 1)⁺ 2.54 (s, 3H), 2.92 (m, 2H),3.37 (t, 2H), 4.02 (t, 2H), 4.33 (m, 2H), 6.87-6.92 (m, 2H), 7.08 (d,1H), 7.12 (s, 1H), 7.42 (d, 1H) 25 398 1.31 (m, 1H), 1.39-1.42 (2x t,3H), 1.68-1.85 (M + 1)⁺ (m, 6H), 2.52 (s, 3H), 2.90 (m, 2H), 3.27-3.43(2 x q, 2H), 4.02-4.14 (m, 2H), 4.25 (m, 2H), 6.75-6.85 (m, 1-2H),6.95-7.21 (m, 3H) 26 Not 0.98 (t, 3H); 1.25-1.55 (m, 3H), 1.80-1.95recorded (m, 6H), 2.61 (s, 3H), 2.85-3.0 (m, 4H), 4.06 (t, 2H), 4.37 (m,2H), 6.88 (dd, 1H), 6.95-7.05 (m, 2H), 7.17 (d, 1H), 7.54 (d, 1H) 27 Not1.06 (t, 3H); 1.35 (m, 1H), 1.80-1.95 (m, 8H), recorded 2.61 (s, 3H),2.85-3.0 (m, 4H), 4.06 (t, 2H), 4.37 (m, 2H), 6.88-6.94 (m, 2H), 7.03(d, 1H), 7.10 (d, 1H), 7.54 (d, 1H) 28 Not 1.25-1.35 (m, 2H), 1.50 (t,3H), 1.73-1.88 (m, recorded 5H), 2.23 (s, 3H), 2.54 (s, 3H), 2.90 (t,2H), 4.03 (t, 2H), 4.32-4.37 (m, 2H), 4.58 (q, 2H), 6.78-6.83 (m, 2H),6.93 (fd, 1H), 7.32 (d, 1H) 29 Not 1.25-1.27 (m, 2H), 1.39 (t, 3H),1.76-1.91 recorded (m, 5H), 2.42 (s, 3H), 3.18 (t, 2H), 3.89-3.93 (m,2H), 4.01 (t, 2H), 4.57 (q, 2H), 6.82 (dd, 1H), 6.92 (fd, 1H), 7.33 (d,1H) 30 398 1.24-1.29 (m, 2H), 1.49 (t, 3H), 1.75-1.86 (M + 1)⁺ (m, 5H),2.33 (s, 3H), 2.46 (s, 3H), 2.92 (t, 2H), 4.03 (t, 2H), 4.58 (q, 2H),4.78-4.83 (m, 2H), 6.81 (dd, 1H), 6.92 (fd, 1H), 7.33 (d, 1H) 31 3731.46-1.52 (m, 5H), 1.78-1.90 (m, 5H), 3.03 (M + 1)⁺ (t, 2H), 3.55-3.59(m, 2H), 3.85 (s, 3H), 4.03 (t, 2H), 4.50 (q, 2H), 6.79 (dd, 1H), 6.91(bd, 1H), 7.32 (d, 1H) 32 Not 1.39-1.43 (m, 2H), 1.50 (t, 3H), 1.77-2.00recorded (m, 5H), 2.36 (s, 3H), 3.08-3.14 (m, 2H), 4.01 (t, 2H),4.45-4.49 (m, 2H), 4.57 (q, 2H), 6.79 (dd, 1H), 6.91 (bd, 1H), 6.98 (s,1H), 7.35 (d, 1H) 33 Not 1.27-1.34 (m, 2H), 1.51 (s, 3H), 1.73-1.88recorded (m, 5H), 2.24 (s, 3H), 2.94 (t, 2H), 4.02 (t, 2H), 4.37-4.42(m, 2H), 4.58 (q, 2H), 6.72 (bs, 1H), 6.83 (dd, 1H), 6.91 (fd, 1H), 7.33(d, 1H), 8.39 (bs, 1H). 34 Not 1.45-1.55 (m, 5H), 1.69-1.82 (m, 4H),2.23 recorded (s, 3H), 2.72 (t, 2H), 3.93 (t, 2H), 4.57 (q, 2H), 5.79(s, 1H), 6.77 (dd, 1H), 6.89 (fd, 1H), 7.31 (d, 1H) 35 383 1.34 (m, 1H);1.50 (t, 3H); 1.80-1.95 (m, 6H); (M + 1)⁺ 2.74 (s, 3H); 3.05 (m, 2H);4.08 (t, 2H); 4.40 (m, 2H); 4.46 (q, 2H); 6.85 (m, 2H); 7.24 (bd, 1H);7.37 (bd, 1H); 7.47 (d, 1H) 36 367 1.34 (m, 2H), 1.43 (t, 3H), 1.82-1.94(m, 5H), (M + 1)⁺ 2.74 (s, 3H), 2.96 (q, 2H), 3.05 (m, 2H), 4.10 (t,2H), 4.40 (m, 2H), 6.89 (dd, 1H), 6.97 (fd, 1H), 7.22 (d, 1H), 7.35 (d,1H), 7.50 (d, 1H) 37 403 1.37 (m, 1H), 1.50 (t, 3H), 1.91 (m, 4H), 3.03(M + 1)⁺ (bt, 2H), 4.08 (t, 2H), 4.39 (bd, 2H), 4.46 (q, 2H), 6.82-6.86(m, 2H), 6.97 (bd, 1H), 7.21 (bd, 1H), 7.47 (d, 1H) 38 397 1.06 (t, 3H),1.34 (m, 3H), 1.81-1.97 (m, 6H), (M + 1)⁺ 2.72 (s, 3H), 3.12 (m, 2H),4.08 (t, 2H), 4.36 (t, 2H), 6.84 (m, 2H), 7.24 (m, 1H), 7.41-7.49 (m,2H) 39 381 1.03 (t, 3H), 1.35 (m, 2H), 1.81-1.94 (m, 7H), (M + 1)⁺ 2.69(s, 3H), 2.90 (t, 2H), 3.03 (t, 2H), 4.10 (t, 2H), 4.36 (m, 2H), 6.89(bd, 1H), 6.96 (s, 1H), 7.14 (bd, 1H), 7.29 (bd, 1H), 7.49 (bd, 1H) 40399 1.36 (m, 2H), 1.48 (t, 3H), 1.79-1.91 (m, 5H), (M + 1)⁺ 2.60 (s,3H), 2.97 (dt, 2H), 4.11 (t, 2H), 4.36 (m, 2H), 4.56 (q, 2H), 6.95 (dd,1H), 6.99 (bd, 1H), 7.14 (fd, 1H), 7.16 (bd, 1H), 7.76 (bd, 1H) 41 Not1.30-1.34 (m, 2H), 1.48 (t, 3H), 1.60-1.70 (m, recorded 1H), 1.84-1.91(m, 4H), 3.04 (t, 2H), 4.01 (t, 2H), 4.39-4.49 (m, 4H), 6.82-6.86 (m,2H), 6.99 (d, 1H), 7.23 (d, 1H), 7.47 (d, 1H) 42 384 1.43 (t, 3H), 2.46(s, 3H), 2.76 (t, 4H), 2.93 (M + 1)⁺ (t, 2H), 3.62 (t, 4H), 4.18 (t,2H), 4.38 (q, 2H), 6.8 (m, 2H), 6.89 (d, 1H), 7.09 (d, 1H), 7.42 (d, 1H)43 Not 1.37 (m, 1H), 1.46 (t, 3H), 1.85-1.92 (m, 6H), recorded 2.66 (s,3H), 3.01 (t, 2H), 4.16 (t, 2H), 4.38 (m, 2H), 4.51 (q, 2H), 7.08 (bd,1H), 7.22-7.26 (m, 1H), 7.32 (m, 1H), 7.34 (fd, 1H), 7.72 (d, 1H), 8.40(s, 1H) 44 418 1.37 (m, 1H), 1.86-1.96 (m, 6H), 2.74 (s, 3H), (M + 1)⁺3.06 (t, 2H), 4.19 (t, 2H), 4.41 (m, 2H), 7.22 (bd, 1H), 7.29 (fd, 1H),7.35 (bd, 1H), 7.43 (dd, 1H), 7.91 (d, 1H) 45 Not 1.36 (m, 1H), 1.50 (2x t, 6H), 1.80-1.94 (m, recorded 6H), 2.68 (s, 3H), 3.02 (m, 2H), 4.13(t, 2H), 4.38 (m, 2H), 4.59 (2 x q, 4H), 7.09 (dd, 1H), 7.11-7.15 (m,1H), 7.15 (fd, 1H), 7.27 (bd, 1H), 7.62 (d, 1H) 46 394 1.37 (m, 2H),1.47 (t, 3H), 1.82-1.95 (m, 5H), (M + 1)⁺ 2.69 (s, 3H), 3.03 (m, 2H),4.18 (t, 2H), 4.39 (m, 2H), 4.52 (q, 2H), 7.13 (bd, 1H), 7.15 (s, 1H),7.15-7.19 (m, 1H), 7.27 (bd, 1H), 7.87 (d, 1H), 8.29 (s, 1H) 47 Not 1.50(t, 3H), 1.55-1.89 (m, 5H), 2.99 (t, 2H), recorded 3.96 (t, 3H),4.35-4.39 (m, 2H), 4.56 (q, 2H), 6.79 (dd, 1H), 6.91-6.96 (m, 2H), 7.21(d, 1H), 7.35 (d, 1H) 48 384 1.49 (t, 3H), 2.54 (s, 3H), 2.81 (m, 4H),2.95 (M + 1)⁺ (t, 2H), 3.71 (m, 4H), 4.21 (t, 2H), 4.58 (q, 2H), 6.84(dd, 1H), 6.86 (d, 1H), 6.95 (fd, 1H), 7.09 (bd, 1H), 7.34 (bd, 1H) 49Not 1.46-1.57 (m, 5H), 1.73-1.85 (m, 4H), 2.25 recorded (s, 3H), 2.73(t, 2H), 3.99 (t, 2H), 4.45 (q, 2H), 5.80 (s, 1H), 6.81-6.84 (m, 2H),7.43 (d, 1H). 50 Not 1.42-1.44 (m, 2H), 1.49 (t, 3H), 1.79-1.86 recorded(m, 5H), 2.56 (s, 3H), 3.08-3.15 (m, 2H), 3.91-3.94 (m, 2H), 4.06 (t,2H), 4.45 (q, 2H), 6.82-6.85 (m, 2H), 7.45 (d, 1H) 51 Not 1.22-1.37 (m,2H), 1.48 (t, 3H), 1.51-1.88 recorded (m, 3H), 2.53 (s, 3H), 2.93 (t,2H), 4.14 (t, 2H), 4.31-4.35 (m, 2H), 4.59 (q, 2H), 6.88 (d, 1H), 7.06(d, 1H), 7.13 (d, 1H), 7.22 (d, 1H), 8.04 (d, 1H), 8.69 (s, 1H) 52 394(CD₃OD) 1.4 (m, 2H); 1.62 (t, 3H); 1.93 (m, (M + H)⁻ 5H); 2.51 (s, 3H);2.99 (m, 2H); 4.35 (m, 4H); 4.52 (q, 2H); 7.24 (d, 1H); 7.31 (d, 1H);7.47 (dd, 1H); 7.64 (d, 1H); 8.19 (d, 1H) and 8.99 (br s 1H) 53 394(CD₃OD) 1.3 (m, 2H); 1.62 (t, 3H); 1.93 (m, (M + H)⁻ 5H); 2.51 (s, 3H);2.99 (m, 2H); 4.32 (m, 2H); 4.38 (m, 2H); 4.52 (q, 2H); 7.23 (d, 1H);7.31 (d, 1H); 7.47 (d, 1H); 7.58 (dd, 1H); 8.27 (d, 1H) and 8.95 (br s1H) 54 Not 1.31-1.43 (m, 2H), 1.52 (t, 3H), 1.82-1.91 (m, recorded 3H),2.55 (s, 3H), 2.95 (t, 2H), 4.16 (t, 2H), 4.32-4.37 (m, 2H), 4.65 (q,2H), 6.87-6.93 (m, 1H), 7.05-7.11 (m, 1H), 7.39 (s, 1H), 7.45 (d, 1H),7.84 (d, 1H), 8.67 (s, 1H) 55 Not 1.29-1.33 (m, 2H), 1.42-1.53 (m, 6H),1.78- recorded 1.89 (m, 5H), 2.52 (s, 3H), 2.93 (t, 2H), 4.08- 4.14 (m,2H), 4.31-4.35 (m, 2H), 4.44 (q, 2H), 4.63 (q, 2H), 6.89 (d, 1H), 7.06(d, 1H), 7.32- 7.37 (m, 2H), 7.58 (d, 1H) 56 384 1.34-1.38 (m, 2H), 1.36(t, 3H), 1.79-1.89 (M + 1)⁺ (m, 5H), 2.59 (s, 3H), 2.96 (dt, 2H), 4.02(q, 2H), 4.08 (t, 2H), 4.36 (m, 2H), 6.64 (fd, 1H), 6.81 (dd, 1H), 6.98(bd, 1H), 7.15 (bd, 1H), 7.67 (d, 1H) 57 397 0.98 (t, 3H), 1.35 (m, 2H),1.78-1.96 (m, 7H), (M + 1)⁺ 2.78 (s, 3H), 3.08 (t, 2H), 3.95 (t, 2H),4.09 (t, 2H), 4.41 (m, 2H), 6.64 (fd, 1H), 6.81 (dd, 1H), 7.50 (bd, 1H),7.41 (bd, 1H), 7.69 (d, 1H) 58 Not 0.96 (t, 3H), 1.4 (m, 3H), 1.68-1.88(m, 6H), recorded 2.11 (q, 2H), 2.52 (s, 3H), 2.92 (m, 2H), 4.06 (t,2H), 4.33 (m, 2H), 4.60 (t, 2H), 6.86 (d, 1H), 7.0-7.1 (m, 3H), 7.08 (d,1H), 7.70 (d, 1H)

Example 18 Anti-HRV Activity in Mammalian Cell Culture Assays

Inhibition of Viral Cytopathic Effect (CPE) and Measurement ofCytotoxicity

The ability of compounds to suppress virus replication and therebyprotect cells from HRV-induced CPE was measured using human embryo lung(MRC-5cells infected with HRV type 1A. Cells grown in 96 well tissueculture plates using conventional mammalian tissue culture medium (suchas minimum essential medium) supplemented with fetal calf serum wereused in an assay essentially similar to that described by Sidwell andHuffman (Applied Microbiology, 22, 797-801 (1971)). Test compounds weredissolved in 100% anhydrous dimethyl sulfoxide and serially diluted intissue culture medium. The antiviral potency of the test compounds wasassessed by exposing replicate tissue culture wells to a selecteddilution series of between 6 and 7 compound concentrations in thepresence of sufficient test virus to invoke significant CPE over thecourse of the assay. Control cells were also exposed to identicalconcentrations of compounds in the absence of virus or were infectedwith virus under the same conditions but in the absence of compounds.Compounds of established anti-HRV efficacy (enviroxime, ribavirin andpirodavir) were assayed by identical procedures in parallel to the testcompounds. Tissue culture media were identically supplemented tomaintain cell viability and support viral growth while suppressingbacterial growth over the period of the assay (supplements: 2% fetalcalf serum, 0.01% sodium bicarbonate, 50 μg/ml gentamicin, 5 μMmagnesium chloride, 10 mM of zinc chloride). The assays were incubatedat 37° C. in a 5% CO₂ atmosphere until significant CPE was observed bymicroscopic examination of the untreated, HRV infected control cells(generally between 5 and 8 days). At this time all infected cultureswere examined by eye using a light microscope and CPE scored on a scaleof 0 (no CPE) to 4 (maximum CPE). Uninfected treated cultures weresimilarly scored for cytotoxic effects (e.g., cell enlargement,granularity, rounding, detachment). These scores were used to generateEC₅₀ (concentration of compound yielding 50% antiviral efficacy) andCC₅₀ (concentration of compound yielding 50% cytotoxicity) values byline regression analysis from plots of compound concentration versus %CPE or % cytotoxicity, respectively. As an alternative to a CC₅₀ value,cytoxicity in some cases was expressed as the Minimum ToxicConcentration (MTC). The MTC corresponds to the lowest compoundconcentration at which cytotoxic effects were observed.

In some cases the visual scoring system described above was validated byvital dye staining to measure cell viability. The vital dye techniqueused was a modification of the method described by McManus (Appl.Environment. Microbiol., 31, 35-38, 1976). After the assay had beenscored by eye with the aid of a microscope, 100 μl of neutral red (NR)solution (0.34% NR in phosphate buffered saline (PBS)) was added to eachwell and mixed gently. The assays were returned to the 37° C. incubatorfor 2 hours to facilitate uptake of the NR by viable cells. Themedium/NR mixture was then aspirated from the surface of the cells,which were washed twice with PBS. 0.25 ml of absolute ethanol containingSorensen's citrate buffer I, was added with gentle mixing and the assaysincubated at room temperature in the dark for 30 minutes to dissolve theNR. NR staining of viable cells was then quantifiedspectrophotometrically by measuring the color density of the NR solutionusing a BioTek EL-309 microplate reader at dual wavelengths of 540 and405 nm. The differences in the two readings were automaticallydetermined to eliminate background errors. EC₅₀ and CC₅₀ values weredetermined by regression analysis matching compound concentration to NRstaining.

The results are shown in the Tables 7 and 8 below. Selectivity indices(SI) are the CC₅₀ or MTC divided by the EC₅₀. Tables 7 and 8 also showIC₅₀ data for the testing of the compounds of the invention against HRVstrains 2 and 14. These results were obtained using a similar CPE methodto that described above for HRV1A.

TABLE 7 IC₅₀ (μg/ml) IC₅₀ (μg/ml) Compound No HRV1A CC₅₀ HRV2 HRV14 10.179 >1 >0.50 >0.50 2 0.120 >1 >0.50 >0.50 3 0.060 >1 0.144 0.130 40.006 >1 0.099 0.047 5 0.003 0.007 6 0.067 0.146 7 0.002 0.006 8 0.0080.020 9 0.061 0.056 10 0.065 0.056 11 0.002 0.020 12 0.159 0.099 130.004 0.015 14 0.024 0.006 15 0.007 0.006

TABLE 8 IC₅₀ (μg/ml) Compound No HRV2 HRV14 16 0.10 0.169 19 0.165 0.04920 0.166 0.041 21 0.104 0.014 22 0.004 0.050 23 0.045 — 24 0.131 >0.25026 0.130 0.082 27 0.075 0.028 28 0.101 0.040 30 >0.250 0.198 310.237 >0.250 32 0.012 0.039 33 0.167 0.166 34 0.209 0.118 35 0.001 0.00536 0.024 0.088 37 0.003 0.019 38 0.003 0.029 39 0.084 0.013 40 0.0030.029 41 0.003 0.009 43 0.012 0.012 46 0.084 0.013 47 0.004 0.010 480.069 0.011 49 0.035 0.012 50 0.007 0.005 51 0.027 0.120 52 0.190 0.20056 0.246 >0.250 57 0.133 0.237 58 0.032 0.139

Throughout this specification and the claims that follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated integer or step or group of integers or steps but not theexclusion of any other integer or step or group of integers or steps.

Those skilled in the art will appreciate that the invention describedherein is susceptible to variations and modifications other than thosespecifically described. It is to be understood that the inventionincludes all such variations and modifications. The invention alsoincludes all of the steps, features, compositions and compounds referredto or indicated in this specification, individually or collectively, andany and all combinations of any two or more of said steps or features.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

1. A compound of formula I

or salt thereof, where: Het is an optionally substituted pyridazineradical; A is O, S, NH, N(C₁₋₆alkyl), CH₂O, a direct bond or a bivalentheterocyclic radical of the formula:

where one or more of the carbon atoms within the radicals (b-1) to (b-4)may be optionally substituted with C₁₋₆alkyl or two carbon atoms in theradicals (b-1) to (b-4) may be bridged with a C₂₋₄alkylene radical, mand n are each independently integers of 1 to 4 inclusive with theproviso that the sum of m and n in radicals (b-1) to (b-4) is 3, 4 or 5;Z is N or CR⁶ where R⁶ is hydrogen, hydroxy, C₁₋₆alkyl, C₁₋₆alkoxy oramino; Z′ is O, S, CHR⁷ or NR⁸ where R⁷ is hydrogen, hydroxy, C₁₋₆alkyl,C₁₋₆alkoxy or amino and R⁸ is hydrogen or C₁₋₆alkyl; R⁴ is hydrogen orC₁₋₆alkyl; R⁵ is hydrogen, hydroxy, C₁₋₆alkyl or C₁₋₆alkoxy; Alk isC₁₋₇alkylene or a direct bond; W is O; X¹, X² and X³ are eachindependently selected from N and CR where R is hydrogen, halogen,hydroxy, C₁₋₆alkyl or C₁₋₆alkoxy; and B is a five or six memberedunsaturated heterocyclic ring, substituted with at least one substituentselected from R¹⁰, OR¹⁰, SR¹⁰ and NR⁹R¹⁰, where R⁹ is hydrogen orC₁₋₆alkyl and R¹⁰ is C₁₋₆alkyl, haloC₁₋₆ alkyl, C₁₋₆alkenyl,haloC₁₋₆alkenyl, C₁₋₆alkynyl or haloC₁₋₆alkynyl, with the proviso thatthe ring bearing B is not benzothiazole, benzimidazole, benzoxazole,benzofused isothiazole, benzofused pyrazole or benzofused isooxazole,and with the proviso that when Alk is a direct bond, then A is not O, S,CH₂O or a direct bond.
 2. A compound according to claim 1 wherein Het is

wherein R¹ is hydrogen, C₁₋₆ alkyl, halo, hydroxy, mercapto,haloC₁₋₆alkyl, amino, mono or di(C₁₋₆ alkyl)amino, cyano, formyl,C₁₋₆alkoxy, hydroxyC₁₋₄ alkyl, C₁₋₄alkoxyC₁₋₄ alkyl, C₁₋₆haloalkoxy,aryloxy, C₁₋₆alkylthio, arylthio, C₁₋₆alkylsulphinyl,C₁₋₆alkylsulphonyl, arylsulphinyl, arylsulphonyl, —CH═NO—C₁₋₄alkyl,C₁₋₆alkyloxycarbonyl, C₁₋₆alkylcarbonyl or aryl; and R² and R³ are eachindependently selected from hydrogen, C₁₋₆alkyl, C₁₋₆alkoxy, or halo, orR¹ and R² or R² and R³ combined represent a bivalent radical of formula—CH═CH—CH═CH— or —(CH₂)_(p)— where p is an integer from 2 to
 4. 3. Acompound according to claim 1 wherein

is selected from

where R¹¹ is R¹⁰, OR¹⁰, SR¹⁰ or NR⁹R¹⁰, where R⁹ and R¹⁰ are as definedin claim
 1. 4. A compound according to claim 2 wherein R¹ is selectedfrom hydrogen, methyl, ethyl, chloro, methoxy and trifluoromethyl.
 5. Acompound according to claim 2 wherein R² and R³ are independentlyhydrogen, chloro or methyl.
 6. A compound according to claim 1 wherein Ais O, NH, NMe, a direct bond or a radical of formula (b-1).
 7. Acompound according to claim 1 wherein Z is CH or N.
 8. A compoundaccording to claim 1 wherein Alk is C₁₋₆alkylene or a direct bond.
 9. Acompound according to claim 1 wherein X¹, X² and X³ are each CH.
 10. Acompound according to claim 3 wherein in (c-3) to (c-11) R¹¹ is selectedfrom methyl, ethyl, n-propyl, n-butyl, methoxy, ethoxy, n-propoxy,methylthio, ethylthio, n-propylamino and chloro.
 11. A compositioncomprising a compound of formula I according to claim 1 or salt thereoftogether with a pharmaceutically acceptable carrier.
 12. Apharmaceutical composition comprising a compound of formula I

or pharmaceutically acceptable salt thereof, together with apharmaceutically acceptable carrier, where: Het is an optionallysubstituted pyridizine radical; A is O, S, NH, N(C₁₋₆alkyl), CH₂O, adirect bond or a bivalent heterocyclic radical of the formula:

where one or more of the carbon atoms within the radicals (b-1) to (b-4)may be optionally substituted with C₁₋₆alkyl or two carbon atoms in theradicals (b-1) to (b-4) may be bridged with a C₂₋₄alkylene radical, mand n are each independently integers of 1 to 4 inclusive with theproviso that the sum of m and n in radicals (b-1) to (b-4) is 3, 4 or 5;Z is N or CR⁶ where R⁶ is hydrogen, hydroxy, C₁₋₆alkyl, C₁₋₆alkoxy oramino; Z′ is O, S, CHR⁷ or NR⁸ where R⁷ is hydrogen, hydroxy, C₁₋₆alkyl,C₁₋₆alkoxy or amino and R⁸ is hydrogen or C₁₋₆alkyl; R⁴ is hydrogen orC₁₋₆alkyl; R⁵ is hydrogen, hydroxy, C₁₋₆alkyl or C₁₋₆alkoxy; Alk isC₁₋₇alkylene or a direct bond; W is O; X¹, X² and X³ are eachindependently selected from N and CR, where R is hydrogen, halogen,hydroxy, C₁₋₆alkyl or C₁₋₆alkoxy; and B is a five or six memberedunsaturated heterocyclic ring, substituted with at least one substituentselected from R¹⁰, OR¹⁰, SR¹⁰ and NR⁹R¹⁰, where R⁹ is hydrogen orC₁₋₆alkyl and R¹⁰ is C₁₋₆alkyl, haloC₁₋₆ alkyl, C₁₋₆alkenyl,haloC₁₋₆alkenyl, C₁₋₆alkynyl or haloC₁₋₆alkynyl, with the proviso thatthe ring bearing B is not benzothiazole, benzimidazole, benzoxazole,benzofused isothiazole, benzofused pyrazole or benzofused isooxazole,and with the proviso that when Alk is a direct bond, then A is not O, S,CH₂O or a direct bond.
 13. A method for the treatment of a humanrhinovirus (HRV) infection in a respiratory tract of a human, comprisingadministering to the human an effective amount of a compound of formulaI

or salt thereof, where: Het is an optionally substituted pyridizineradical; A is O, S, NH, N(C₁₋₆alkyl), CH₂O, a direct bond or a bivalentheterocyclic radical of the formula:

where one or more of the carbon atoms within the radicals (b-1) to (b-4)may be optionally substituted with C₁₋₆alkyl or two carbon atoms in theradicals (b-1) to (b-4) may be bridged with a C₂₋₄alkylene radical, mand n are each independently integers of 1 to 4 inclusive with theproviso that the sum of m and n in radicals (b-1) to (b-4) is 3, 4 or 5;Z is N or CR⁶ where R⁶ is hydrogen, hydroxy, C₁₋₆alkyl, C₁₋₆alkoxy oramino; Z′ is O, S, CHR⁷ or NR⁸ where R⁷ is hydrogen, hydroxy, C₁₋₆alkyl,C₁₋₆alkoxy or amino and R⁸ is hydrogen or C₁₋₆alkyl; R⁴ is hydrogen orC₁₋₆alkyl; R⁵ is hydrogen, hydroxy, C₁₋₆alkyl or C₁₋₆alkoxy; Alk isC₁₋₇alkylene or a direct bond; W is O; X¹, X² and X³ are eachindependently selected from N and CR, where R is hydrogen, halogen,hydroxy, C₁₋₆alkyl or C₁₋₆alkoxy; and B is a five or six memberedunsaturated heterocyclic ring, substituted with at least one substituentselected from R¹⁰, OR¹⁰, SR¹⁰ and NR⁹R¹⁰, where R⁹ is hydrogen orC₁₋₆alkyl and R¹⁰ is C₁₋₆alkyl, haloC₁₋₆ alkyl, C₁₋₆alkenyl,haloC₁₋₆alkenyl, C₁₋₆alkynyl or haloC₁₋₆alkynyl, with the proviso thatthe ring bearing B is not benzothiazole, benzimidazole, benzoxazole,benzofused isothiazole, benzofused pyrazole or benzofused isooxazole,and with the proviso that when Alk is a direct bond, then A is not O, S,CH₂O or a direct bond.
 14. A compound of claim 1 having the structure:

or salt thereof.
 15. A compound of claim 1 having the structure:

or salt thereof.
 16. A compound of claim 1 having the structure:

or salt thereof.
 17. A compound of claim 1 having the structure:

or salt thereof.
 18. A compound of claim 1 having the structure:

or salt thereof.
 19. A compound of claim 1 having the structure:

or salt thereof.
 20. A compound of claim 1 having the structure:

or salt thereof.
 21. A compound of claim 1 having the structure:

or salt thereof.
 22. A compound of claim 1 having the structure:

or salt thereof.
 23. A compound of claim 1 having the structure:

or salt thereof.